JPH07333092A - Amplification rate variable device and inner pressure detection device, electromagnetic induction type displacement detector, and tire air pressure sensor of traveling body - Google Patents

Abstract

PURPOSE:To provide an electromagnetic induction displacement detector which can accurately detect displacement with a simple circuit configuration regardless of the frequency fluctuation of a carrier signal and at the same time provide an electromagnetic induction type tire air pressure sensor which can accurately detect tire air pressure and its change regardless of the change in vehicle speed. CONSTITUTION:A magnetic flux change generation means 2 modulates the amplitude of alternate magnetic flux according to the displacement in a movable body and an amplitude compensation means (low-pass filter) 4 attenuates the amplitude of the electromagnetic induction voltage of a pickup coil 3 with an attenuation rate which is nearly proportional to the amplitude of an electromagnetic induction voltage. When the frequency (carrier frequency) of the alternate magnetic flux fluctuates, the amplitude of the electromagnetic induction voltage fluctuates proportionately with the frequency. However since the amplitude of the electromagnetic induction voltage is attenuated with an attenuation rate which is nearly proportional to the frequency, the amplitude of the electromagnetic induction voltage does not change almost at all regardless of the change in the frequency (carrier frequency of electromagnetic induction voltage) of alternate magnetic flux and hence an accurate displacement can be detected according to the amplitude change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplification factor varying device capable of changing the amplification factor according to frequency, an internal pressure detecting device for a moving body, and an electromagnetic induction for detecting a displacement in a non-contact manner using the electromagnetic induction principle. Type displacement detection device and a tire air pressure sensor using this electromagnetic induction type displacement detection device.

[0002]

2. Description of the Related Art An electromagnetic induction type displacement detecting device is provided which includes a magnetic flux change generating means for changing the amount of magnetic flux interlinking with a pickup coil according to the displacement as well as the displacement of a movable body to be detected. It has an advantage that its displacement can be detected without contacting the movable body.

Further, as an application example of this electromagnetic induction type displacement detecting device, a tire air pressure sensor for detecting that a permanent magnet built in a tire is displaced by tire air pressure as a magnetic flux change generating means by a pickup coil on the vehicle side is also known. Has been.

[0004]

However, the above-mentioned conventional electromagnetic induction type displacement detection device and the tire air pressure sensor using the same have the following problems. That is, when this electromagnetic induction type displacement detection device or the like detects the above displacement by amplitude modulation (AM) of a carrier signal of variable frequency,
The amplitude of the detection voltage electromagnetically induced in the pickup coil changes according to the fluctuation of the frequency of the carrier signal (carrier),
The amplitude change due to the frequency change of the carrier signal is superimposed on the original amplitude change corresponding to the displacement of the movable body, and as a result, the amplitude of the movable body is determined by the amplitude of the signal voltage electromagnetically induced in the pickup coil. It was difficult to do.

Therefore, in the above-described conventional tire air pressure sensor, there is a device for rapidly changing the flux linkage amount of the pickup coil by rotating, for example, a permanent magnet at a predetermined position of displacement of the movable body (a predetermined tire air pressure value). is doing. However, such a binary tire pressure detection has a drawback in that it cannot perform an operation such as knowing in advance that the tire pressure approaches a predetermined limit level.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an amplification factor varying device and an electromagnetic induction type displacement detecting device capable of accurately detecting a displacement despite frequency fluctuations of a carrier signal. Has an aim. Another object of the present invention is to provide an internal pressure detection device for a moving body and an electromagnetic induction type tire air pressure sensor capable of accurately detecting tire air pressure and its change despite changes in vehicle speed.

Another object of the present invention is to achieve the above object with a simple circuit configuration. Further, the present invention has another object to achieve the effects described below.

[0008]

The first structure of the present invention is as follows.
Output generating means for outputting a signal in which the frequency and the magnitude of the output signal change, and frequency filter means for inputting the signal from the output generating means and varying the amplification factor according to the frequency of the signal by means of the attenuation characteristic portion An amplification factor varying device characterized by comprising:

A second structure of the present invention is characterized in that, in the first structure, the frequency filter means is a low-pass filter. A third configuration of the present invention is characterized in that, in the first configuration, the frequency filter means is a high pass filter.
A fourth configuration of the present invention is the same as the first configuration,
The frequency filter means is a bandpass filter.

A fifth structure of the present invention is characterized in that, in any one of the first to third structures, the frequency of the input signal is set to a cutoff frequency of the frequency filter means. A sixth configuration of the present invention is further characterized in that, in the first configuration, the output signal from the output generating means is an electromagnetic induction signal.

According to a seventh aspect of the present invention, a pressure detecting means for detecting a change in internal pressure of the moving body as a change in magnetic flux, and an amplifier for adjusting a signal from the means so as to change an amplification factor according to its frequency. An internal pressure detecting device for a moving body, comprising: a rate varying means; and a signal processing means for processing an output signal adjusted and outputted by the varying means to determine an internal pressure of the moving body. .

According to an eighth structure of the present invention, in addition to the above-mentioned seventh structure, the variable means changes the amplification factor according to the frequency of the output signal from the pressure detection means by the attenuation characteristic. It is characterized in that frequency filter means is provided. According to a ninth configuration of the present invention, in addition to the seventh or eighth configuration, the pressure detecting means further comprises a magnet whose position changes according to a change in the internal pressure of the moving body, and a magnetic force of the magnetic pole of the magnet. It is characterized in that it includes a pressure sensor portion composed of a magnet whose position changes.

A tenth structure of the present invention is the above seventh to ninth embodiments.
In any one of the above configurations, the signal processing means further comprises
It is characterized in that the magnitude of the internal pressure of the moving body is judged in at least two stages or more by comparing the adjusted output signal with at least one threshold value. An eleventh configuration of the present invention is the configuration according to any one of the seventh to ninth configurations, wherein the signal processing means uses the magnitude of the adjusted output signal as a signal. It is characterized by being output.

A twelfth structure of the present invention is the seventh to the first above.
In any one of the configurations of 1 and 2, the moving body is a tire of an automobile. 13th of the present invention
In the configuration, a pickup coil, a magnetic flux change generating means for performing amplitude modulation of an alternating magnetic flux which is displaced in association with a movable body whose displacement is to be detected and which interlinks with the pickup coil according to the displacement, and a frequency substantially Amplitude correction means for attenuating the amplitude of the electromagnetic induction voltage of the pickup coil with a proportional attenuation rate is provided.

A fourteenth structure of the present invention is the above thirteenth structure, wherein the amplitude correction means is a low-pass filter, and the carrier frequency of the alternating magnetic flux is such that the output signal amplitude is substantially proportional to the frequency. It is characterized in that it is set within the attenuation band of the low-pass filter which is attenuated by. A fifteenth structure of the present invention is the same as the thirteenth structure, wherein when the attenuation rate is a predetermined proportional constant value K,
It is characterized in that it is set in the range of 0.5K to 2K.

In a sixteenth structure of the present invention, in addition to any one of the thirteenth to fifteenth structures, the amplitude correction means further negatively feeds back the output voltage through a parallel feedback circuit of a shunt resistor Rs and a feedback capacitor C. The carrier frequency f is set to a value larger than fc = 1 / (2πRsC). In a seventeenth configuration of the present invention, the magnetic flux change generating means is fixed to a tire, is fixed to the fixed magnet, and is held by the tire so as to be displaceable on the fixed magnet. A movable magnet whose distance from the fixed magnet changes, and a rotary magnet which is positioned between the two magnets and is rotatably held and is rotated by the displacement of the movable magnet due to the magnetic force of the movable magnet and the fixed magnet. Any one of the above-mentioned thirteenth to sixteenth configurations is used which is configured to generate a carrier signal interlocked with a vehicle speed, and an electromagnetic induction voltage having an amplitude according to the vehicle speed and the displacement, in the pickup coil, which is composed of a dynamic magnet. It is characterized in that it is composed of a tire pressure sensor.

An eighteenth structure of the present invention is characterized in that, in the seventeenth structure, a tire air pressure signal corresponding to the amplitude of the output signal of the amplitude correction means is output. A nineteenth structure of the present invention is the same as the eighteenth structure, further including a comparison means for converting a tire pressure signal corresponding to the amplitude of the output signal of the amplitude correction means into a multi-step signal, and a display for displaying the comparison result. And means.

[0018]

In the first configuration of the present invention, even when the signal input to the amplification factor varying device has a property that its magnitude changes depending on the frequency, the amplification factor varying device of the present invention. As a result, a signal having a constant level can be obtained, and a stable output can be obtained regardless of the frequency. On the contrary, it is possible to obtain the signal corresponding to the frequency by the amplification factor varying device of the present invention when the input signal has a constant magnitude regardless of the frequency.

In the second structure of the present invention, the input signal can be increased in size with frequency, but can be set to a constant level, and a stable output can be obtained regardless of frequency. You can get it. Conversely, a signal whose magnitude does not change depending on the frequency can be converted into a signal whose magnitude decreases as the frequency increases by the amplification factor varying device of the present invention.

In the third configuration of the present invention, the input signal can be reduced in magnitude with frequency, but can be set to a constant level, and a stable output can be obtained regardless of frequency. You can Conversely, a signal whose magnitude does not change depending on the frequency can be converted into a signal whose magnitude increases as the frequency increases by the amplification factor varying device of the present invention.

In the fourth structure of the present invention, an input signal has two or more frequency bands, and a signal of a certain level is obtained for the characteristics that the signal becomes large or the invention becomes small depending on the frequency bands. be able to. On the contrary, it is possible to obtain a signal whose magnitude increases or decreases according to the frequency in the frequency band. In the fifth configuration of the present invention, for a signal having a frequency higher or lower than the assumed frequency band of the input signal,
It is possible to prevent further amplification, and it is possible to prevent excessive output of the circuit used in the subsequent stage.

In the sixth structure of the present invention, since the magnetic flux generated from the moving body is converted into the signal voltage by using the electromagnetic induction, it is possible to obtain a stable output of the signals of various detecting devices regardless of the moving speed. it can. With the seventh to ninth configurations of the present invention, it is possible to obtain an air pressure detection device that can obtain an output that changes the output of the air pressure sensor attached to the moving body only by the air pressure regardless of the moving speed.

Further, in the tenth to twelfth configurations of the present invention, since the air pressure signal can be output in multiple stages or its absolute value, the state of the air pressure can be recognized more accurately. In the thirteenth configuration of the present invention, the magnetic flux change generation means amplitude-modulates the alternating magnetic flux according to the displacement of the movable body, and the amplitude correction means
The amplitude of the electromagnetic induction voltage of the pickup coil is attenuated at an attenuation rate substantially proportional to the frequency.

Frequency of alternating magnetic flux (also called carrier frequency)
, The amplitude of the electromagnetic induction voltage fluctuates in proportion to the frequency.However, in this configuration, the amplitude of the electromagnetic induction voltage is attenuated at a damping rate that is approximately proportional to the frequency. The amplitude of the electromagnetic induction voltage hardly changes regardless of the change of the carrier frequency of the voltage, and the displacement can be accurately detected by the change of the amplitude.

In the fourteenth structure of the present invention, in addition to the thirteenth structure, the carrier frequency of the alternating magnetic flux is set within the attenuation band of the low pass filter in which the output signal amplitude attenuates substantially in proportion to the frequency. The amplitude correction means can be configured with a simple low-pass filter. In the fifteenth configuration of the present invention, when the predetermined proportional constant value is K in the carrier signal band to be detected in the thirteenth configuration, the attenuation factor is set in the range of 0.5K to 2K. In the carrier signal band to be detected, the amplitude of the electromagnetic induction voltage can be made substantially constant with respect to the fluctuation of the carrier signal frequency, and as a result, the displacement can be accurately detected by the amplitude of the electromagnetic induction voltage.

In the sixteenth structure of the present invention, the thirteenth to the thirteenth embodiments are
In any one of the fifteenth configuration, the shunt resistor R
Since the amplitude correction means is configured by the integrating circuit that negatively feeds back the output voltage through the parallel feedback circuit of s and the feedback capacitance C, and the carrier frequency f is set to a value larger than fc = 1 / (2πRsC), Saturation can be prevented and linear amplification can be performed for a low frequency component or a direct current component of a small electromagnetic induction voltage (including a change frequency of the flux linkage amount due to the displacement of the movable body), while it is larger than fc. With respect to the frequency component (including the frequency of the alternating magnetic flux, that is, the carrier frequency), the amplitude can be attenuated by the integral operation in proportion to the magnitude of the carrier frequency.

In the seventeenth or eighteenth structure of the present invention, the rotating magnet is rotated by the combined magnetic field of the movable magnet and the fixed magnet displaced by the change of the tire air pressure to change the amount of the interlinking magnetic flux. Even before the turning time, the amount of the interlinkage magnetic flux is changed by the displacement of the movable magnet or the small turning of the turning magnet affected by the displacement. Therefore, although the amplitude of the corrected signal output from the amplitude correction means changes in conjunction with the displacement of the movable magnet before the signal voltage change due to the large rotation of the rotating magnet, it changes due to the vehicle speed change (carrier frequency change). There is almost no change, and as a result, the displacement of the movable magnet can be accurately detected before the large rotation of the rotating magnet.

In the nineteenth structure of the present invention, the tire pressure signal corresponding to the amplitude of the output signal of the amplitude correcting means is further displayed in multiple stages in the eighteenth structure, so that the driver can easily reduce the tire pressure. It is possible to recognize the state, and it is possible to accurately recognize that the tire air pressure has reached a predetermined value (for example, pressure supplement is required) due to the rotation of the rotating magnet.

[0029]

【Example】

<Embodiment> An embodiment of an automobile tire air pressure sensor which is also an application example of the electromagnetic induction type displacement detection device of the present invention will be described below with reference to the drawings. FIG. 1 shows a perspective view of this tire pressure sensor.

A rim 11 of the tire 1 is fixed to an axle (not shown), and a hub 13 holding the axle is supported by a vehicle body (not shown) through a shock absorber (not shown). The rim 11 is fixed with the magnet portion 2 of the tire air pressure sensor (magnetic flux change generating means in the present invention), and the hub 13 is fixed with the pickup coil 3 so as to be close to the magnet portion 2.

The output voltage (electromagnetic induction voltage) Vp of the pickup coil 3 is processed by a compensation amplifier 4 and a signal processing circuit 5, which will be described later, and is displayed as a tire pressure on the display 6 in multiple levels. The magnet unit 2 will be described with reference to FIG. Both end openings of the cylindrical case 20 are closed by lids 21 and 22, and the lids 21 and 22 have shafts 21a and 22a, respectively, which project inward along the axis.
A bellows 23 is fitted on the shaft portion 22a,
The base end portion of is fixed to the base portion of the shaft portion 22a. A holder 24 is fixed to the tip of the bellows 23, and the holder 24 is slidably guided along the inner peripheral surface of the cylindrical case 20. The shaft portion 22a is formed with a hole through which tire air pressure is introduced, whereby the bellows 23 is urged by the tire air pressure so as to extend to the left in the figure. A movable magnet 25 is fixed to the holder 24. Further, the spring 26, whose base end is supported by the shaft portion 21a, urges the holder 24 to the right in the drawing, so that the holder 24 stands still at a point where the above two forces oppose each other.

On the other hand, the fixed magnet 2 is attached to the base end of the shaft portion 21a.
7 is fitted and fixed, and a rotating magnet 28 is rotatably held in the center of the shaft portion 21a so as not to be displaced in the axial direction. The movable magnet 25, the fixed magnet 27, and the rotating magnet 28 each have a thick wheel plate shape, and the movable magnet 25 is magnetized so that the upper portion has an N pole and the lower portion has an S pole in the drawing. The fixed magnet 27 is magnetized so that the upper part has an S pole and the lower part has an N pole in the figure. The rotating magnet 28 is a fixed magnet 27.
Is arranged at a predetermined distance in the axial direction from.

When the movable magnet 25 is separated from the rotating magnet 28, the rotating magnet 28 is moved by the magnetic field of the fixed magnet 27 as shown in FIG.
As shown in the figure, the upper part of the drawing is held in a posture in which it is an N pole and the lower part is an S pole. On the other hand, the movable magnet 25 is the rotating magnet 2
8, when the magnetic field of the fixed magnet 27 is reached, the movable magnet 25
The magnetic field of 1 becomes stronger than that of the rotating magnet 28, and as a result, the rotating magnet 28 is rotated by half, and is held in a posture in which the lower portion is the N pole and the upper portion is the S pole.

Since the magnet portion 2 rotates together with the tire 1, a part of the magnetic flux leaking from the magnet portion 2 interlinks with the pickup coil 3 for each rotation of the tire 1, and the pickup coil 3 has one cycle of AC voltage waveform. Will be output. Then, due to the above rotation of the rotary magnet 28, the shape of the AC voltage waveform of this one cycle is different in 180 degree phase. That is, the order of the positive half-wave and the negative half-wave of the AC voltage waveform of one cycle is reversed. This tire air pressure sensor detects whether or not the tire air pressure has become equal to or lower than a predetermined value by using the above principle.

Next, the electromagnetic induction voltage of the pickup coil 3 will be further described. Before and after the rotation of the rotating magnet 28, the amount of magnetic flux leaking from the surface of the rotating magnet 28 toward the pickup coil 3 decreases, so that the amount of interlinkage magnetic flux of the pickup coil 3 decreases as the tire air pressure decreases. It gradually decreases, and the amount of interlinkage magnetic flux at the time when the rotation reaches 90 degrees becomes the minimum, and after that,
The amount of interlinkage magnetic flux increases again. As a result, the peak value (or the half-wave rectification value, or more specifically, the absolute value) of the electromagnetic induction voltage of the pickup coil 3 at a constant vehicle speed changes following the change in air pressure.

However, the peak value of the electromagnetic induction voltage of the pickup coil 3 changes substantially in proportion to the vehicle speed. FIG. 4 shows the waveform of the electromagnetic induction voltage V at a vehicle speed of 10 km / h, and FIG. 5 shows the electromagnetic induction voltage V at a vehicle speed of 200 km / h.
Shows the waveform of. Theoretically, the ratio of electromagnetic induction voltage at both vehicle speeds is 20 times, but due to various losses, it is actually 0.
It is 15V, 2V vs. 3.0V.

When the tire pressure monitor is operated in the range of 10 km / h to 200 km / h, the tire rotation speed is 1.5 rps to 30 rps. According to the measurement, at this time, one cycle time (cycle) of the electromagnetic induction voltage of the pickup coil 3 could be considered to be 4 ms to 60 ms. Here, one cycle time (cycle) is defined as the time between both ends when the electromagnetic induction voltage becomes 1/20 of its peak value. In this specification, the reciprocal of this one cycle time is regarded as the frequency of this electromagnetic induction voltage (carrier frequency in the present invention). Therefore, the carrier frequency is from 17Hz to 25
It becomes 0 Hz.

FIG. 6 shows the measured results of the vehicle speed, the carrier frequency and the peak value of the electromagnetic induction voltage. Both have a substantially direct proportional relationship as described above. In FIG. 7, the pickup coil 3
An example of the compensation amplifier 4 for improving the frequency characteristic of the output voltage of is shown. The compensation amplifier 4 includes an operational amplifier 40, a feedback circuit including a parallel circuit of a shunt resistor Rs and a feedback capacitor C, an offset compensation resistor R2 connecting the + input terminal of the operational amplifier 40 and the ground, and a negative input of the operational amplifier 40. Input resistor R1 for connecting the end and one end of the pickup coil 3
Consists of. The other end of the pickup coil 3 is grounded. In this example, R1 was set to 93 KΩ, Rs was set to 6.3 KΩ, and C was set to 0.1 μF.

The compensating amplifier 4 is an ordinary integrating circuit (low-pass filter), and its DC amplification factor is -Rs / R1.
Is. As is well known, in this integration circuit,
When the frequency f of the input signal voltage is smaller than fc = 1 / (2πRsC), it becomes a mere inverting amplifier and the frequency f becomes f.
When it exceeds c, it becomes an integrator. In this embodiment, fc is set to 10 Hz as shown in FIG. 8, and the peak value of the output voltage of the compensation amplifier 4 is set to about 2 V regardless of the vehicle speed.

That is, the band as an integrator of the compensating amplifier 4 (hereinafter also referred to as a stop band) is overlapped with the carrier signal band, and the signal band (pneumatic signal band, 0.1 Hz or less) is used as a linear amplifier of the compensating amplifier 4. (Hereinafter, also referred to as a linear amplification band or a pass band) is overlapped with the carrier signal band. In the band (stop band) as the integrator, the output voltage of the compensation amplifier 4 is almost inversely proportional to the frequency,
It is possible to compensate for the variation in the peak value of the electromagnetic induction voltage V due to the variation in the vehicle speed described above so that it is substantially independent of the frequency. On the other hand, for the amount of interlinkage magnetic flux corresponding to the air pressure, linear amplification can be performed by the amplifier characteristic of the pass band. Further, in this embodiment, since a low-pass filter having a very low cutoff frequency is used as the compensation amplifier 4, various AC noise voltage components (for example, almost all electromagnetic noise induced in the pickup coil 3 can be cut). As a result, it is possible to obtain a tire pressure signal whose SN ratio is extremely high and whose amplitude does not vary depending on the vehicle speed.

FIG. 9 shows a signal processing circuit 5 for processing the compensated signal voltage Vc output from the compensation amplifier 4 and outputting it to the display 6. The signal voltage Vc is output from the comparators 51 to
55, and the output signals S1 to S5 thereof are input to the logic circuit section 56. The comparators 54 and 55 are for determining whether the rotating magnet 28 is rotating before or after rotating. Before and after rotating, the comparators 54 and 55 have a + half wave and a −half wave of one cycle waveform of the electromagnetic induction voltage. Since the order of the half-waves is reversed, this is discriminated to determine before and after the rotation.

The comparator 54 binarizes the + half wave with the threshold voltage Vrefa, and the comparator 5
Reference numeral 5 denotes a binary half-wave with a threshold voltage Vrefb. The logic circuit unit 56 outputs a high level (turn signal) when the output voltage S4 appears before the output voltage S5. Before the movement is completed) is output, and when the output voltage S5 appears before the output voltage S4, a low level (after the completion of the rotation) is output as the rotation determination signal.

On the other hand, the comparators 51 to 53 each judge whether or not the peak of + half-wave exceeds it, and accordingly, the change of the interlinkage magnetic flux amount, that is, the displacement of the movable magnet 25, that is, the change of the tire air pressure. Is determined (see FIG. 3). As shown in FIG. 3, the logic circuit unit 56 includes the rotation determination signal and the comparators 51 to 53.
According to the comparison results S1 to S3, the six tire air values a to
f can be determined, and these six levels are output to the light-emitting display 6 that displays different colors. (Modification) As the magnetic flux change generating means, any means may be used as long as it changes the amount of magnetic flux interlinking with the pickup coil 3 according to the change in tire air pressure.

As the compensating amplifier 4, in addition to the above low-pass filter, if it is a circuit having a 1 / f characteristic in the carrier frequency band and a constant transmission efficiency in the tire air pressure change frequency band (almost DC), Other circuits may be used. For example, it is also possible to employ a variable gain amplifier in which the frequency of the electromagnetic induction voltage is extracted and the amplification factor is controlled in inverse proportion to this frequency. However, in this case, the circuit configuration becomes complicated and power consumption increases.

Further, in the above-described embodiment, the description has been given by taking the automobile tire as an example of the moving body, but the internal pressures of not only the tire but also other moving objects can be detected in a non-contact manner by the same method. Further, the moving body to be detected is not limited to the rotary moving body, and may be a linear moving body or a non-linear moving body.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing the overall configuration of a tire air pressure sensor of this embodiment.

2 is a cross-sectional view of a magnet unit 2 of FIG.

3 is a diagram showing the relationship between the peak value of the electromagnetic induction voltage of the pickup coil 3 of FIG. 1 and the tire pressure.

FIG. 4 is a waveform diagram of an electromagnetic induction voltage.

FIG. 5 is a waveform diagram of an electromagnetic induction voltage.

FIG. 6 is a diagram showing a relationship between a vehicle speed and a carrier frequency and a peak value of an electromagnetic induction voltage.

FIG. 7 is a circuit diagram of a compensation amplifier 4.

FIG. 8 is a diagram showing a frequency-gain relationship of the compensation amplifier 4.

9 is a block diagram of a signal processing circuit 5. FIG.

FIG. 10 is a waveform diagram showing the relationship between the output voltage waveform of the compensation amplifier 4 and each threshold voltage.

[Explanation of symbols]

1 is a tire, 2 is a magnet part (flux change generating means), 3 is a pickup coil, 4 is a compensating amplifier (amplitude correcting means),
5 is a signal processing circuit, 25 is a movable magnet, 27 is a fixed magnet,
28 is a rotating magnet.

Claims (19)

[Claims] 1. An output characteristic means for outputting a signal whose frequency and a magnitude of an output signal change, and a signal from the output generation means are inputted, and a variable amplification factor corresponding to the frequency of the signal is used as an attenuation characteristic portion. An amplification factor varying device, comprising: 2. The amplification factor varying device according to claim 1, wherein the frequency filter means is a low-pass filter. 3. The amplification factor varying device according to claim 1, wherein the frequency filter means is a high-pass filter. 4. The amplification factor varying device according to claim 1, wherein said frequency filter means is a bandpass filter. 5. The amplification factor varying device according to claim 1, wherein the frequency of the input signal is set to a cutoff frequency of the frequency filter means. 6. The amplification factor varying device according to claim 1, wherein the output signal from said output generating means is an electromagnetic induction signal. 7. A pressure detecting means for detecting a change in internal pressure of a moving body as a change in magnetic flux, an amplification factor changing means for adjusting a signal from the means so as to change an amplification factor according to the frequency, and the variable. An internal pressure detecting device for a mobile body, comprising: a signal processing means for processing an output signal adjusted and output by the means to determine the internal pressure of the mobile body. 8. The variable means comprises frequency filter means for changing the amplification factor according to the frequency of the output signal from the pressure detecting means by means of an attenuation characteristic. Internal pressure detection device for moving objects. 9. The pressure detecting means includes a pressure sensor section including a magnet whose position changes in accordance with a change in internal pressure of the moving body and a magnet whose magnetic pole position changes due to the magnetic force of the magnet. The internal pressure detection device for a moving body according to claim 7 or 8, wherein: 10. The signal processing means judges the magnitude of the internal pressure of the moving body in at least two stages by comparing the adjusted output signal with at least one threshold value. Claims 7 to 9 characterized
The internal pressure detection device for a moving body according to any one of claims. 11. The signal processing means outputs the magnitude of the internal pressure of the moving body as a signal according to the magnitude of the adjusted output signal. The internal pressure detection device for a moving body according to any one of the above. 12. The internal pressure detection device for a moving body according to claim 7, wherein the moving body is a tire of an automobile. 13. A pickup coil, a magnetic flux change generating means for amplitude-modulating an alternating magnetic flux which is displaced in association with a movable body whose displacement is to be detected, and which interlocks with the pickup coil according to the displacement. An electromagnetic induction type displacement detection device, comprising: an amplitude correction unit that attenuates the amplitude of the electromagnetic induction voltage of the pickup coil with a substantially proportional attenuation rate. 14. The amplitude correction means comprises a low pass filter, and the carrier frequency of the alternating magnetic flux is set within the attenuation band of the low pass filter where the output signal amplitude is attenuated at the attenuation rate substantially proportional to the frequency. Item 13. An electromagnetic induction type displacement detection device according to Item 13. 15. The attenuation rate is set in a range of 0.5K to 2K, where K is a predetermined proportional constant value.
The electromagnetic induction type displacement detection device described. 16. The amplitude correcting means comprises a shunt resistor Rs.
The carrier frequency f is fc = 1.
14. A value larger than / (2πRsC) is set.
16. The electromagnetic induction type displacement detection device according to any one of 1 to 15. 17. The magnetic flux change generating means includes a fixed magnet fixed to a tire, a fixed magnet facing the fixed magnet and displaceably held by the tire, and the fixed magnet depending on an air pressure of the tire. A movable magnet whose distance between the two magnets changes, and a rotating magnet which is located between the two magnets and is rotatably held and which is rotated by the displacement of the movable magnets due to the magnetic force of the movable magnets and the fixed magnets. The electromagnetic induction displacement detection device according to any one of claims 13 to 16, wherein an electromagnetic induction voltage having an amplitude corresponding to the vehicle speed and the vehicle speed and the displacement is generated in the pickup coil. Tire pressure sensor using. 18. The tire air pressure sensor according to claim 17, which outputs a tire air pressure signal corresponding to the amplitude of the output signal of the amplitude correction means. 19. The tire air pressure sensor according to claim 18, further comprising: comparing means for converting a tire air pressure signal corresponding to the amplitude of the output signal of the amplitude correcting means into a multi-step signal, and display means for displaying the comparison result. .